Periodontitis is a destructive, infectious disease that has been associated with multiple fatal and debilitating chronic systemic diseases and consumes billions of dollars in health costs annually in the US. Tobacco smokers exhibit increased susceptibility to periodontitis; are more likely to be infected with the key periodontal pathogen Porphyromonas gingivalis; and to harbor higher numbers of this bacterial species relative to non-smokers. Despite this, smokers consistently exhibit reduced clinical inflammation. We show that the pro-inflammatory response of purified human monocytes is significantly suppressed when P. gingivalis is exposed to cigarette smoke extracts (CSE) and that the inflammation inducing potential of P. gingivalis is restored when cells are sub-cultured back into fresh medium without CSE. However, the influence of tobacco on the regulation of genes encoding P. gingivalis virulence determinants is essentially unknown. We hypothesize that CSE represents an environmental stress and that P. gingivalis responds by altering gene expression to adapt to this stress. We believe that this adaptive response may involve the induction of stress-related genes, virulence determinants and alterations of bacterial surface components. We also hypothesize that such cigarette smoke-induced physiological changes in P. gingivalis will include altered activities of genes encoding key pathogen recognition determinants, which will explain the reduced inflammatory response of smoke-exposed P. gingivalis. It is our aim to identify, isolate and test CSE-altered gene products in a primary human monocyte model of inflammation. Preliminary data generated through transcriptome analyses and the structural characterization of several microbial determinants are strongly supportive of our hypotheses. We have identified several genes, gene products, and bacterial structures that are dysregulated on CSE exposure that may play pivotal roles in the engagement of the innate immune system by P. gingivalis. These include fimbrial proteins, LPS, major outer membrane antigens, and other P. gingivalis components of known inflammatory potential, such as dnaJ, grpE and ragA. These studies represent a novel area of investigation and will provide some of the first information illustrating how P. gingivalis responds at the molecular level to cigarette smoke and may provide unique insights into disease pathogenesis in smokers. Thus, these studies will break new ground and provide the foundation for future studies that will elucidate mechanisms explaining how tobacco influences pathogen-host response interactions.